JPMorgan Chase's $2 billion trading loss has renewed concerns about how the nation's largest banks manage risk and raised doubt as to whether the 2010 financial overhaul adequately protects taxpayers. Overnight, CEO Jamie Dimon seems to have gone from exhibit A in the case that too-big-to-fail banks can be safely run without tighter regulatory handcuffs to exhibit A that they can't. In one respect, the shift may be unwarranted: The